McIntyre says self-control can be the deal-maker for people considering a foray into polygamy.

"If you have strong desires to stray and an inability to control those desires, then it creates a perfect storm that may lead to infidelity," he says.

"Of course, it's not just self-control and desire.

"There are characteristics of the relationship that can trigger infidelity. For example, frequent arguments, lack of trust, long-distance relationships and stifling the personal development of one's partner are all associated with higher rates of infidelity."

Dating forums like AshleyMadison and eHarmony can often be the trigger for extra-marital affairs, McIntyre says.

"The websites simply make it easier for people to act on their pre-existing sexual desires," he says.

"They mean that people can find available partners from the comfort of their living room or office."